Using a track format code in a cache control block for a track in a cache to process read and write requests to the track in the cache

ABSTRACT

Provided are a computer program product, system, and method for using a track format code in a cache control block for a track in a cache to process read and write requests to the track in the cache. A track format table associates track format codes with track format metadata. A determination is made as to whether the track format table has track format metadata matching track format metadata of a track staged into the cache. A determination is made as to whether a track format code from the track format table for the track format metadata in the track format table matches the track format metadata of the track staged. A cache control block for the track being added to the cache is generated including the determined track format code when the track format table has the matching track format metadata.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a computer program product, system, andmethod for using a track format code in a cache control block for atrack in a cache to process read and write requests to the track in thecache.

2. Description of the Related Art

In a storage environment, a host system may communicate a read/writerequest to a connected storage system over network channel through anetwork adaptor. If the data is in a cache of the storage system, i.e.,a read hit, then the data may be returned quickly to the host system.This reduces the delay in returning requested data to a host I/Orequest. However, if the requested data is not in the cache of thestorage system, then there may be significant latency realized while thestorage system needs to retrieve the requested data from storage toreturn. Further, the thread or task executing the host read request mayhave to be context switched and deactivated in order to allow the hostsystem to process further I/O requests. When the data is returned to theread request, then the task must be reactivated and data for the taskmust be returned to registers and processor cache to allow processing ofthe returned data for the read request.

There is a need in the art for improved techniques for processing hostread/write requests to the cache.

SUMMARY

In a first embodiment, provided are a computer program product, system,and method for using a track format code in a cache control block for atrack in a cache to process read and write requests to the track in thecache. A track format table associates track format codes with trackformat metadata, wherein each of the track format metadata indicates alayout of data in a track. A track is staged from the storage into thecache and track format metadata for the track staged into the cache isprocessed. A determination is made as to whether the track format tablehas track format metadata matching the track format metadata of thetrack staged to the cache. A determination is made as to whether a trackformat code from the track format table for the track format metadata inthe track format table matches the track format metadata of the trackstaged into the cache in response to the track format table having thematching track format metadata. A cache control block for the trackbeing added to the cache is generated including the determined trackformat code when the track format table has the matching track formatmetadata.

With the first embodiment, a track format code is added to the cachecontrol block for a track in the cache to use to determine the tracklayout and format when processing the track in the cache by looking upthe track format metadata for the track format code in the track formattable. This provides fast access to the track format metadata for atrack in cache without having to read and process track metadata for thetrack from the storage. This fast access to the track format metadatasubstantially reduces the latency for processing read and write requestsbecause reading track metadata to determine the track format metadata isa substantial component of read/write processing latency.

In a second embodiment, the first embodiment may additionally includethat a read or write request to a target track is received from the hoston a first channel connecting to the host. A determination is made as towhether the target track is in the cache. A determination is made as towhether the cache control block for the target track includes a validtrack format code from the track format table in response to determiningthat the target track is in the cache. The read or write request isfailed in response to determining that the target track is not in thecache or determining that the cache control block does not include avalid track format code. The failing the read or write request causesthe host to resend the read or write request to the target track on asecond channel connecting to the host.

With the second embodiment, if the read or write request is received ona channel requiring fast response time, such as if the request is senton a bus interface where the host thread for the read/write request isspinning on the request while waiting for a response, the request isfailed if there is no valid track format code for the track in thecache. If there is no valid track format code, then the response willnot be able to satisfy time requirements for a fast access channelbecause the track metadata will need to be accessed to determine thetrack format. However, if there is a valid track format code, then therequest can be responded to within the timing requirements for the fastchannel because there will be minimal latency to determine the trackformat metadata from the track format table using the track format codein the cache control block.

In a third embodiment, the second embodiment may additionally include afirst channel that provides faster processing of the read or writerequest than the second channel.

With the third embodiment, the track format table allows fast processingfor the fast channel by providing the track format codes to use todetermine the track format metadata for a track.

In a fourth embodiment, the second embodiment may additionally includethat a read or write request to the target track is received on a secondchannel connected to the host after failing the read or write requestfor the target track when the target track is not in the cache. At leastone of the operations of the staging the target track into the cache,the processing the track format metadata, the determining whether thetrack format table has the matching track format metadata, thedetermining the track format code, and the generating the cache controlblock are performed in response to receiving the read or write requeston the second channel.

With the fourth embodiment, if the request on the fast channel is failedbecause there is no valid track format code for the target track in thecache control block, then the request is resent on a slower secondchannel where the host thread managing the I/O request would havecontext switched because of the expected longer time for the requestresponse on the second channel. In such case, when the request isreceived on the slower channel, then the request will be processed whenthere is no valid track format code for the target track, which willrequire at least one of staging the target track into cache and readingthe track metadata to determine track format metadata, which may be usedto determine the track format code to include in the cache control blockto reduce latency for future requests toward the track.

In a fifth embodiment, the second embodiment may additionally includethat a read or write request to the target track is received on thesecond channel connected to the host after failing the read or writerequest for the target track having the cache control block thatincludes an invalid track format code. In response to receiving the reador write request on the second channel when the cache control block forthe target track does not have a valid track format code, track formatmetadata is read for the target track to process the read or writerequest received on the second channel. A determination is made as towhether the track format table has track format metadata matching theread track format metadata. A determination is made of a track formatcode from the track format table for the matching track format metadatain response to the track format table having the matching track formatmetadata. The determined track format code is included in the cachecontrol block for the target track as a valid track format code.

With the fifth embodiment, when the request for the target track isreceived on the slower second channel after failing the request on thefaster first channel, the track format metadata is then read and a trackformat code determined and included in the cache control block to allowfor fast processing of the read/write request on the second channel forfuture requests to the target track, so that the track format metadatacan be quickly determined without having to read track metadata fromstorage for future requests.

In a sixth embodiment, the first embodiment may additionally includethat the cache control block includes a valid flag indicating whetherthe cache control block includes a valid track format code. The validflag is set to valid when adding the track format code to the cachecontrol block. A write to update a track in the cache is received whenthere is a cache control block for the track to update in the cacheincluding a track format code. A determination is made as to whether theupdate to the track modifies a track format. The valid flag is set toindicate invalid in response to determining that the update to the trackmodifies the track format.

With the sixth embodiment, a valid track format code is used to indicatewhether the track format code in a cache control block is valid. Thisflag is set to invalid when the track format is changed by a writeoperation, because in such circumstance the track format code in thecache control block no longer accurately represents the track format ofthe track, which was changed by the update. The valid track format codeprovides information that allows for a fast determination of whether thecache control block includes a valid track format code that can be usedto process the read or write request.

In a seventh embodiment, provided are a computer program product, systemand method for managing read and write requests from a host to tracks instorage cached in a cache. A track format table associated track formatcodes with track format metadata, wherein each of the track formatmetadata indicates a layout of data in a track. In cache control blocksfor tracks in the cache, at least one cache control block of the cachecontrol blocks include one of the track format codes in the track formattable indicating the track format metadata for the track. A read orwrite request to a target track is received from the host in the cache.A determination is made as to whether the cache control block for thetarget track includes a valid track format code. The track formatmetadata is determined for the valid track format code from the trackformat table in response to determining that the cache control blockincludes the valid track format code. The determined track formatmetadata is used to process the read or write request to the targettrack in the cache.

With the seventh embodiment, when the cache control block for a targettrack includes a valid track format code, then the track format metadatafor the target track can be quickly determined from the track formattable without having to read the track metadata from the storage. Thisuse of the track format table substantially reduces the latency inprocessing read and write requests to target tracks.

In an eighth embodiment, provided are a computer program product, systemand method for managing read and write requests from a host to tracks instorage cached in a cache. A track format table associates track formatcodes with track format metadata, wherein each of the track formatmetadata indicates a layout of data in a track. A read or write requestto a target track in the cache is received from the host on one of afirst channel and a second channel connecting to the host. Adetermination is made as to whether a cache control block for the targettrack includes a valid track format code in the track format table. Theread or write request is failed in response to determining that thecache control block does not include the valid track format code whenthe read or write request is received on the first channel. The trackformat metadata for the valid track format code is determined from thetrack format table in response to determining that the cache controlblock includes the valid track format code. The determined track formatmetadata is used to process the read or write request to the targettrack in the cache.

With the eight embodiment, if the read/write request is received on thechannel requiring fast processing, then the request is failed if thecache control block for the target track does not include the trackformat code because the latency introduced by having to read the trackmetadata will not allow the request on the first channel to completewithin a required time. However, if the cache control block includes avalid track format code, then the request on the first channel can beprocessed because the response can be returned within the required timefor the first channel when the track format metadata can be determinedfrom the track format table.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a storage environment.

FIG. 2 illustrates an embodiment of a track format table entry.

FIG. 3 illustrates an embodiment of a cache control block.

FIG. 4 illustrates an embodiment of a Least Recently Used (LRU) list oftracks in the cache.

FIG. 5 illustrates an embodiment of operations to process a read/writerequest received on a first channel, such as a bus interface.

FIG. 6 illustrates receive an embodiment of operations to process aread/write request received on a second channel, such as a network.

FIG. 7 illustrates an embodiment of operations to close track metadataand determine a track format code for the track in cache of the closedtrack metadata.

FIG. 8 illustrates an embodiment of a computer architecture used withdescribed embodiments.

DETAILED DESCRIPTION

In a storage environment, a host system may first communicate aread/write request to a connected storage system over a fast channel,such as a bus interface, such as the Peripheral Component InterconnectExpress (PCIe) interface. For a read/write request over the fast channelwhich is supposed to complete within a threshold time, the host systemholds the application thread for the read/write request in a spin loopwaiting for the request to complete. This saves processor timeassociated with a context swap, which deactivates the thread andreactivates the thread in response to an interrupt when a response tothe read/write request is received. If the data for the read/writerequest sent on the fast channel is not in cache, then the storagesystem may fail the read/write request and the host system maycommunicate the same read/write request over a storage area network viaa host adaptor, which is slower than processing the I/O request over thebus, e.g., PCIe interface. Communicating the read/write request over thesecond channel requires the host system to perform a context switch fromthe task handling the read/write request to another task while waitingfor the read/write request to complete. Context switching is costlybecause it requires the processor running the task to clear allregisters and L1 and L2 caches for the new task, and then whencompleting the new task, reactivate the context switched task and returnthe state data to the registers and L1 and L2 caches for the task thatwas context switched while waiting for the read/write request tocomplete.

Certain read/write operations need to be completed within a thresholdtime, else they are failed. The storage system will have to access trackmetadata to process a request to a track. The track metadata providesinformation on the format of data and layout of records in the trackthat are needed in order to perform reads and writes to the track.However, the reading of the track metadata from the storage comprises asubstantial portion of the latency in processing read/write request.Described embodiments provide improvements to cache technology thatreduce cache operation latency by including a track format code in thecache control block for a track in the cache. This track format code maybe used for fast access to the track format from a track format tablewithout having to read the track metadata from storage. By eliminatingthe need to read the track metadata from a metadata track in storage todetermine the track layout, described embodiments increase thelikelihood that read/write requests on the first channel that need to becompleted within a threshold time are completed by accessing the tracklayout information for a track from the track format table, associatingtrack format codes with track format information for common trackformats.

With described embodiments, a read/write request to a target track on achannel requiring that the request be completed within a threshold timeis processed if the track format code for the target track is within thecache control block for the target track. Using the track format code toaccess the track format metadata from the track format table reduces thelatency of access to the track format metadata to allow the read/writerequest to complete within the time threshold. This keeps the time thehost thread is spinning on the read/write request task for theread/write request sent on the bus interface within an acceptable timethreshold. However, if the cache control block for the target track doesnot have a valid track format code, then the read/write request on thefirst channel is failed because it is unlikely the read/write requestcan complete within the threshold time given that the track formatmetadata will have to be retrieved from the storage. Failing theread/write request on the first channel, causes the host to redrive theread/write request on the second channel. The processing of theread/write request on the second channel reads in the track metadatafrom the storage to allow for processing the read/write request andadding the track format code to the cache control block for the targettrack.

FIG. 1 illustrates an embodiment of a storage environment in which ahost 100 directs read and write requests to a storage system 102 toaccess tracks in volumes configured in storage devices 104 in a diskenclosure 106. The host 100 includes a processor complex 108 of one ormore processor devices and a memory 110 including an operating system111 executed by the processor complex 108. The host operating system 111generates read and write requests to tracks configured in the storagedevices 104. The host 100 includes hardware to communicate read andwrite requests on two different channels. A first channel is a businterface, such as a Peripheral Component Interconnect Express (PCIe),including a bus 112, a bus switch 114 to connect one or more devices onthe bus 112, including the processor complex 108, a memory system 110,and a bus host adaptor 116 to extend the bus interface over an externalbus interface cable 118 to the storage system 102. Additional businterface technology to extend the bus interface may be utilized,including PCIe extender cables or components, such as a distributed PCIeswitch, to allow PCIe over Ethernet, such as with the ExpEthertechnology. A second channel to connect the host 100 and storage system102 uses a network host adaptor 120, connected to the bus 112, thatconnects to a separate network 122 over which the host 100 and storagesystem 102 additionally communicate. The first channel through the businterface may comprise a faster access channel than the network 122interface through the network host adaptor 120.

The storage system 102 includes a bus interface comprising a bus 124 a,124 b, a bus switch 126 to connect to endpoint devices on the bus 124 a,124 b, and a bus host adaptor 128 to connect to the external businterface cable 118 to allow communication over the bus interface to thehost 100 over the first channel. The storage system 102 includes anInput/Output bay 130 having the bus host adaptor 128, one or more deviceadaptors 132 to connect to the storage devices 104, and one or morenetwork host adaptors 134 to connect to the network 122 and hostsystems.

The storage system 102 includes a processor complex 136 of one or moreprocessor devices and a memory 138 having a cache 140 to cache tracksaccessed by the connected hosts 100. The memory 138 includes a cachemanager 142 and a storage manager 144. The storage manager 144 managesaccess requests from processes in the hosts 100 and storage system 102for tracks in the storage 104. The devices 136, 138, 128, 132, and 134connect over the bus interface implemented in the bus lanes 124 a, 124 band bus switch 126.

The cache manager 142 maintains accessed tracks in the cache 140 forfuture read access to the tracks to allow the accessed tracks to bereturned from the faster access cache 140 instead of having to retrievefrom the storage 104. Further, tracks in the cache 140 may be updated bywrites. A track may comprise any unit of data configured in the storage104, such as a track, Logical Block Address (LBA), etc., which is partof a larger grouping of tracks, such as a volume, logical device, etc.

The cache manager 142 maintains cache management information 146 in thememory 138 to manage read (unmodified) and write (modified) tracks inthe cache 140. The cache management information 146 may include a trackformat table 200 having track format codes for common track formatdescriptors providing details of a layout and format of data in a track;track index 148 providing an index of tracks in the cache 140 to cachecontrol blocks in a control block directory 300; and a Least RecentlyUsed (LRU) list 400 for tracks in the cache 140. The control blockdirectory 300 includes the cache control blocks, where there is onecache control block for each track in the cache 140 providing metadataon the track in the cache 140. The track index 148 associates trackswith the cache control blocks providing information on the tracks in thecache 140. Upon determining that the cache LRU list 400 is full or hasreached a threshold level, tracks are demoted from the LRU list 400 tomake room for more tracks to stage into the cache 140 from the storage104.

In certain embodiments, there may be multiple hosts 100 that connect tothe storage system 102 over the first and second channels to accesstracks in the storage devices 104. In such case, the storage system 102would have at least one bus host adaptor 128 to connect to the businterface 118 of each connected host 100 and one or more network hostadaptors 134 to connect to the network host adaptors 120 on the hosts100.

In one embodiment, the bus interfaces 112, 114, 116, 118, 124 a, 124 b,126, and 128 may comprise a Peripheral Component Interconnect Express(PCIe) bus interface technology. In alternative embodiments, the businterfaces 112, 114, 116, 118, 124 a, 124 b, 126, and 128 may utilizesuitable bus interface technology other than PCIe. The bus host adaptors116 and 128 may comprise PCIe host adaptors that provide the interfaceto connect to the PCIe cable 118. The network 122 may comprise a StorageArea Network (SAN), a Local Area Network (LAN), a Wide Area Network(WAN), the Internet, an Intranet, etc., and the network host adaptors120, 134 provide the network 122 connections between the hosts 100 andstorage system 102.

The storage system 102 may comprise a storage system, such as theInternational Business Machines Corporation (IBM®) DS8000® and DS8880storage systems, or storage controllers and storage systems from othervendors. (IBM and DS8000 are trademarks of International BusinessMachines Corporation throughout the world). The host operating system111 may comprise an operating system such as Z Systems Operating System(Z/OS®) from International Business Machines Corporation (“IBM”) orother operating systems known in the art. (Z/OS is a registeredtrademark of IBM throughout the world).

The storage devices 104 in the disk enclosure 106 may comprise differenttypes or classes of storage devices, such as magnetic hard disk drives,solid state storage device (SSD) comprised of solid state electronics,EEPROM (Electrically Erasable Programmable Read-Only Memory), flashmemory, flash disk, Random Access Memory (RAM) drive, storage-classmemory (SCM), etc., Phase Change Memory (PCM), resistive random accessmemory (RRAM), spin transfer torque memory (STT-RAM), conductivebridging RAM (CBRAM), magnetic hard disk drive, optical disk, tape, etc.Volumes in a storage space may further be configured from an array ofdevices, such as Just a Bunch of Disks (JBOD), Direct Access StorageDevice (DASD), Redundant Array of Independent Disks (RAID) array,virtualization device, etc. Further, the storage devices 104 in the diskenclosure 106 may comprise heterogeneous storage devices from differentvendors and different types of storage devices, such as a first type ofstorage devices, e.g., hard disk drives, that have a slower datatransfer rate than a second type of storage devices, e.g., SSDs.

FIG. 2 illustrates an embodiment of a track format table entry 200 _(i)in the track format table 200, which includes a track format code 202and the track format metadata 204. In certain embodiments Count Key Data(CKD) track embodiments, the track format metadata 204 may comprise atrack format descriptor (TFD) indicating a number of records in thetrack, a block size, a number of blocks in the track, a data length ofeach of the records, and a control interval size indicating an amount ofdata that is read or written atomically as a unit, number of blocks in acontrol interval, and whether a control interval spans two tracks, andother information. The track format code 202 may comprise an index valueof the index entry 200 _(i) in the track format table 200. For instance,if there are 32 track format table entries 200 _(i), then the trackformat code 202 may comprise 5 bits to reference the different possiblenumber of 32 entries 200 _(i).

FIG. 3 illustrates an embodiment of a cache control block 300 _(i) forone of the tracks in the cache 140, including, but not limited to, acache control block identifier 302, such as an index value of the cachecontrol block 300 _(i); a track ID 304 of the track in the storage 104;the cache LRU list 306 in which the cache control block 300 _(i) isindicated; an LRU list entry 308 at which the track is indicated; acache timestamp 310 indicating a time the track was added to the cache140 and indicated on the LRU list 306; additional track metadata 312typically maintained for tracks stored in the cache 140, such as a dirtyflag indicting whether the track was modified; a track format code 314comprising one of the track format codes 202 of the track formatmetadata 204 describing the layout of data in the track 304 representedby the cache control block 300 _(i); a track format code valid flag 316indicating whether the track format code 314 is valid or invalid; and aninvalid reason 318 indicating a reason for the track format code validflag 316 code being invalid, as indicated in the track format code validflag 316.

FIG. 4 illustrates an embodiment of an LRU list 400 _(i), such as havinga most recently used (MRU) end 402 identifying a track most recentlyadded to the cache 140 or most recently accessed in the cache 140 and aleast recently used (LRU) end 404 from which the track identified at theLRU end 404 is selected to demote from the cache 140. The MRU end 402and LRU end 404 point to track identifiers, such as a track identifieraddress or a cache control block index for the track, of the tracks thathave been most recently added and in the cache 140 the longest,respectively, for tracks indicated in that list 400.

FIG. 5 illustrates an embodiment of operations performed by the cachemanager 142 and storage manager 144 to process a read/write request to atarget track received on a first fast channel, such as the PCIe businterface via bus host adaptor 128. Upon receiving (at block 500) theread/write request at the bus host adaptor 128, if (at block 502) thetarget track is not in the cache 140, then the storage manager 144returns (at block 504) fail to the read/write request on the firstchannel or bus host adaptor 128 to the host 100, which causes the host100 to retry the read/write request on the second channel or networkhost adaptor 120, 134. Failure is returned because if the target trackis not in the cache 140, then the target track and track metadata needsto be staged into cache 140, which would likely exceed the timethreshold for read/writes on the first channel, where the host processoris spinning on the thread of the read/write request. If (at block 502)the target track is in the cache 140 is a write and if (at block 508)the write modifies the track format, then the cache manager 142 sets (atblock 510) the track format code valid flag 316 to invalid and indicates(at block 512) the invalid reason 318 that the track in the cache 140was invalidated as track format change. The storage manager 144 thenreturns (at block 504) fail to the host 100 because the track metadataneeds to be read from the storage 104 to update with the modified trackformat.

If (at block 506) the read/write request is a read or if (at block 508)the request is a write that does not modify the track format, then thecache manager 142 determines (at block 514) if the track format codevalid flag 316 is set to valid. If so, then the cache manager 142determines (at block 516) the track format metadata 204 in the trackformat table 200 corresponding to the track format code 314 in the cachecontrol block 300 _(i). The cache manager 142 uses (at block 518) thetrack format layout indicated in the determined track format metadata204 to process the read or write request to the target track in thecache 140. If the request is a write, a dirty flag 312 in the cachecontrol block 300 _(i) may be set to indicate the track is modified. If(at block 514) the track format code valid flag 316 is invalid, meaningthere is no fast access to track format information available throughthe track format code 314, then the storage manager 144 returns (atblock 504) fail on the bus interface to the bus host adaptor 128 becausethe track format table 200 cannot be used, and the track metadata needsto be read from the storage 104, which would introduce too much latencyfor the fast read/write on the first channel.

With the embodiment of operations of FIG. 5 , during a fast write overthe bus interface or first channel, if the track format metadata may beaccessed without latency through the track format table 200, then theread/write request is allowed to proceed when the transaction can beprocessed very quickly because the track metadata can be obtaineddirectly from the track format table 200 through the track format code314, without having to read the track metadata from storage 104.However, if the cache control block 300 _(i) does not have a valid trackformat code 314 to allow low latency access of track format metadata,then the read/write request is failed because the transaction will notlikely complete within a fast time threshold. This determination isimportant to avoid host delays in processing other tasks while the hostprocessor is spinning on the thread handling the read/write requestwhile waiting for the read/write request to complete. If the trackmetadata can be accessed from the track format table 200 than there is ahigh likelihood the read/write can complete on the bus interface channelwithin the time required to avoid the host processor holding the threadfor too long, which causes other I/O requests to be queued and delayed.If the track metadata cannot be accessed from the track format table 200and needs to be read from the storage 104, then it is unlikely theread/write request will complete within the time threshold for the hostprocessor to spin on the thread for the read/write request, and failureis returned. Returning failure when the track metadata cannot beobtained from the track format table 200 causes the host thread waitingon the read/write request task to be deactivated and the host processormay context switch to processing other tasks, and then the read/writerequest is retried on the second network channel during the contextswitch.

FIG. 6 illustrates an embodiment of operations performed by the cachemanager 142 and storage manager 144 to process a read/write request to atarget track received on a second channel, such as the network 122 onnetwork host adaptor 134. Upon receiving (at block 600) the read/writerequest, if (at block 602) the target track is not in the cache 140,then the cache manager 142 stages (at block 604) the track from thestorage 104 to the cache 140 and reads (at block 606) the track metadatafor the target track from the storage 104 to determine the track format,e.g., size of blocks, control interval, layout of records on the track,etc. If (at block 608) the read/write request is a write and if (atblock 610) the write modifies the track format, then the cache manager142 updates (at block 612) the track metadata to indicate the modifiedtrack format and sets (at block 614) the track format code valid flag316 to invalid. The track metadata 312 is further updated (at block 616)to indicate the track is modified or dirty. If (at block 608) therequest is a read or from block 616, the cache manager 142 uses (atblock 618) the track format layout indicated in the track formatmetadata to process the read or write request to the target track in thecache 140.

If (at block 602) the target track is in the cache 140 and if (at block630) the track format code valid flag 316 is set to valid, then thecache manager 142 determines (at block 632) the track format metadata204 in the track format table 200 corresponding to the track format code314 in the cache control block 300 _(i) for the target track. From block632, control proceeds to block 608 to process the read/write request. If(at block 630) the track format code valid flag 316 is set to invalid,then control proceeds to block 606 to read the metadata for the trackform the storage 104 to determine the track format layout.

With the embodiment of FIG. 6 , when the read/write request is receivedon the second slower channel, such as over the network 122, where thehost operating system 111 would have performed a context switch for thethread handling the read/write request, the cache manager 142 may readthe track metadata from the storage 104 to determine the track layout toprocess the request. During this time, the host processing of furtherhost requests is not delayed because the host thread handling theread/write request is context switched and not active, until theread/write request returns complete.

FIG. 7 illustrates an embodiment of operations performed by the cachemanager 142 when closing the track metadata for a track in the cache140, which involves destaging the track metadata to the storage 104 ifchanged. Upon closing (at block 700) the track metadata for a track inthe cache 140, the cache manager 142 processes (at block 702) the trackmetadata to determine a track format or a layout of data in the track.If (at block 704) the track format table 200 does not have a trackformat metadata 204 matching the determined track format from the trackmetadata, which may happen if the determined track format is irregular,then the track format code valid flag 316 is set (at block 706) toinvalid and the invalid reason 318 is set to indicate that the trackformat is not supported. In such situation, read/write requests to thetrack having an irregular format are only processed when receivedthrough the second channel via network host adaptor 134.

If (at block 704) the track format table has a track format metadata 204matching the determined track format from the track metadata, then thecache manager 142 determines the track format code 202 for thedetermined track format metadata 204 in the track format table 200 andincludes the track format code 202 in the field 314 in the cache controlblock 300 _(i). The track format code valid flag 316 is set (at block716) to valid. From block 708 or 716, control proceeds to block 718 todestage the track metadata from the memory 138 if modified or discard ifnot modified.

With the operations of FIG. 7 , the track format information may beindicated in the cache control block 300 _(i) with a track format code202 having a limited number of bits to index track format metadata 204describing track layout in a track format table 200, where the trackmetadata itself would not fit into the cache control block 300 _(i). Forfuture read/write accesses, if a valid track format code 314 isprovided, then the cache manager 142 may use that code 314 to obtainwith low latency the track format metadata 204 from the track formattable 200 without having to read the track metadata from the storage 104and process to determine the track format.

The present invention may be implemented as a system, a method, and/or acomputer program product. The computer program product may include acomputer readable storage medium (or media) having computer readableprogram instructions thereon for causing a processor to carry outaspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The computational components of FIG. 1 , including the host 100 andstorage system 102 may be implemented in one or more computer systems,such as the computer system 802 shown in FIG. 8 . Computer system/server802 may be described in the general context of computer systemexecutable instructions, such as program modules, being executed by acomputer system. Generally, program modules may include routines,programs, objects, components, logic, data structures, and so on thatperform particular tasks or implement particular abstract data types.Computer system/server 802 may be practiced in distributed cloudcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed cloud computing environment, program modules may be locatedin both local and remote computer system storage media including memorystorage devices.

As shown in FIG. 8 , the computer system/server 802 is shown in the formof a general-purpose computing device. The components of computersystem/server 802 may include, but are not limited to, one or moreprocessors or processing units 804, a system memory 806, and a bus 808that couples various system components including system memory 806 toprocessor 804. Bus 808 represents one or more of any of several types ofbus structures, including a memory bus or memory controller, aperipheral bus, an accelerated graphics port, and a processor or localbus using any of a variety of bus architectures. By way of example, andnot limitation, such architectures include Industry StandardArchitecture (ISA) bus, Micro Channel Architecture (MCA) bus, EnhancedISA (EISA) bus, Video Electronics Standards Association (VESA) localbus, and Peripheral Component Interconnects (PCI) bus.

Computer system/server 802 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 802, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 806 can include computer system readable media in the formof volatile memory, such as random access memory (RAM) 810 and/or cachememory 812. Computer system/server 802 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 813 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 808 by one or more datamedia interfaces. As will be further depicted and described below,memory 806 may include at least one program product having a set (e.g.,at least one) of program modules that are configured to carry out thefunctions of embodiments of the invention.

Program/utility 814, having a set (at least one) of program modules 816,may be stored in memory 806 by way of example, and not limitation, aswell as an operating system, one or more application programs, otherprogram modules, and program data. Each of the operating system, one ormore application programs, other program modules, and program data orsome combination thereof, may include an implementation of a networkingenvironment. The components of the computer 802 may be implemented asprogram modules 816 which generally carry out the functions and/ormethodologies of embodiments of the invention as described herein. Thesystems of FIG. 1 may be implemented in one or more computer systems802, where if they are implemented in multiple computer systems 802,then the computer systems may communicate over a network.

Computer system/server 802 may also communicate with one or moreexternal devices 818 such as a keyboard, a pointing device, a display820, etc.; one or more devices that enable a user to interact withcomputer system/server 802; and/or any devices (e.g., network card,modem, etc.) that enable computer system/server 802 to communicate withone or more other computing devices. Such communication can occur viaInput/Output (I/O) interfaces 822. Still yet, computer system/server 802can communicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 824. As depicted, network adapter 824communicates with the other components of computer system/server 802 viabus 808. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with computersystem/server 802. Examples, include, but are not limited to: microcode,device drivers, redundant processing units, external disk drive arrays,RAID systems, tape drives, and data archival storage systems, etc.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims herein after appended.

What is claimed is:
 1. A computer program product for managing read andwrite requests from a host to tracks in storage cached in a cache, thecomputer program product comprising a computer readable storage mediumhaving computer readable program code embodied therein that isexecutable to perform operations, the operations comprising: maintaininga track format table including track format codes to associate withtrack format metadata, wherein instances of the track format metadataindicate layouts of data in tracks; including track format codes fromthe track format table in cache control blocks for tracks in the cacheto indicate the track format metadata for the tracks; and failing arequest to a track in response to determining that a cache control blockfor the requested track does not include a valid track format code. 2.The computer program product of claim 1, wherein the operations furthercomprise: failing the request to the requested track in response todetermining that the requested track is not in the cache.
 3. Thecomputer program product of claim 1, wherein the cache control blocksinclude track format code valid flags indicating whether the trackformat codes in the cache control blocks are valid or invalid, whereinthe operations further comprise: failing the request to the requestedtrack in response to determining that there is a cache control block forthe requested track and a track format code valid flag in the cachecontrol block that indicates a track format code for the requested trackis invalid.
 4. The computer program product of claim 1, wherein thecache control blocks include track format code valid flags indicatingwhether the track format codes in the cache control blocks are valid orinvalid, wherein the operations further comprise: setting a track formatcode valid flag in a cache control block for a track in the cache inresponse to closing track metadata and determining that there is a trackformat code for a track format of the track in the closed trackmetadata; and setting the track format code valid flag to indicateinvalid in response to an update to a track modifying a track format ofthe updated track.
 5. The computer program product of claim 1, whereinthe cache control blocks include track format code valid flagsindicating whether the track format codes in the cache control blocksare valid or invalid, wherein the operations further comprise: settinginvalid reason bits in a cache control block in response to a writerequest to modify a format of a track.
 6. The computer program productof claim 1, wherein the request for the requested track comprises afirst request and is failed in response to the first request sent on afirst channel, wherein the operations further comprise: receiving asecond request for the requested track on a second channel after failingthe first request on the first channel; staging the requested track intothe cache in response to the second request and determining that therequested track is not in the cache; and reading metadata for therequested track to determine a track format of the requested trackstaged into the cache to process the request in response to the requestcomprising a read request.
 7. The computer program product of claim 1,wherein the request for the requested track comprises a first requestand is failed in response to the first request sent on a first channel,wherein the operations further comprise: receiving a second request forthe requested track on a second channel after failing the first requeston the first channel; staging the requested track into the cache inresponse to determining that the requested track is not in the cache andin response to the second request; and indicating the track format codein the cache control block as invalid in response to a write request onthe second channel that modifies a track format of the requested trackstaged into the cache.
 8. A system for managing read and write requestsfrom a host to tracks in storage, comprising: a processor; a cache tocache tracks from the storage; a computer readable storage medium havingcomputer readable program code embodied therein that is executable toperform operations, the operations comprising: maintaining a trackformat table including track format codes to associate with track formatmetadata, wherein instances of the track format metadata indicatelayouts of data in tracks; including track format codes from the trackformat table in cache control blocks for tracks in the cache to indicatethe track format metadata for the tracks; and failing a request to atrack in response to determining that a cache control block for therequested track does not include a valid track format code.
 9. Thesystem of claim 8, wherein the operations further comprise: failing therequest to the requested track in response to determining that therequested track is not in the cache.
 10. The system of claim 8, whereinthe cache control blocks include track format code valid flagsindicating whether the track format codes in the cache control blocksare valid or invalid, wherein the operations further comprise: failingthe request to the requested track in response to determining that thereis a cache control block for the requested track and a track format codevalid flag in the cache control block that indicates a track format codefor the requested track is invalid.
 11. The system of claim 8, whereinthe cache control blocks include track format code valid flagsindicating whether the track format codes in the cache control blocksare valid or invalid, wherein the operations further comprise: setting atrack format code valid flag in a cache control block for a track in thecache in response to closing track metadata and determining that thereis a track format code for a track format of the track in the closedtrack metadata; and setting the track format code valid flag to indicateinvalid in response to an update to a track modifying a track format ofthe updated track.
 12. The system of claim 8, wherein the cache controlblocks include track format code valid flags indicating whether thetrack format codes in the cache control blocks are valid or invalid,wherein the operations further comprise: setting invalid reason bits ina cache control block in response to a write request to modify a formatof a track.
 13. The system of claim 8, wherein the request for therequested track comprises a first request and is failed in response tothe first request sent on a first channel, wherein the operationsfurther comprise: receiving a second request for the requested track ona second channel after failing the first request on the first channel;staging the requested track into the cache in response to the secondrequest and determining that the requested track is not in the cache;and reading metadata for the requested track to determine a track formatof the requested track staged into the cache to process the request inresponse to the request comprising a read request.
 14. The system ofclaim 8, wherein the request for the requested track comprises a firstrequest and is failed in response to the first request sent on a firstchannel, wherein the operations further comprise: receiving a secondrequest for the requested track on a second channel after failing thefirst request on the first channel; staging the requested track into thecache in response to determining that the requested track is not in thecache and in response to the second request; and indicating the trackformat code in the cache control block as invalid in response to a writerequest on the second channel that modifies a track format of therequested track staged into the cache, maintaining a track format tableincluding track format codes to associate with track format metadata,wherein instances of the track format metadata indicate layouts of datain tracks; including track format codes from the track format table incache control blocks for tracks in cache to indicate the track formatmetadata for the tracks; and failing a request to a track in response todetermining that a cache control block for the requested track does notinclude a valid track format code.
 15. A method for managing read andwrite requests from a host to tracks in storage cached in a cache,comprising: maintaining a track format table including track formatcodes to associate with track format metadata, wherein instances of thetrack format metadata indicate layouts of data in tracks; includingtrack format codes from the track format table in cache control blocksfor tracks in the cache to indicate the track format metadata for thetracks; and failing a request to a track in response to determining thata cache control block for the requested track does not include a validtrack format code.
 16. The method of claim 15, further comprising:failing the request to the requested track in response to determiningthat the requested track is not in the cache.
 17. The method of claim15, wherein the cache control blocks include track format code validflags indicating whether the track format codes in the cache controlblocks are valid or invalid, further comprising: failing the request tothe requested track in response to determining that there is a cachecontrol block for the requested track and a track format code valid flagin the cache control block that indicates a track format code for therequested track is invalid.
 18. The method of claim 15, wherein thecache control blocks include track format code valid flags indicatingwhether the track format codes in the cache control blocks are valid orinvalid, further comprising: setting a track format code valid flag in acache control block for a track in the cache in response to closingtrack metadata and determining that there is a track format code for atrack format of the track in the closed track metadata; and setting thetrack format code valid flag to indicate invalid in response to anupdate to a track modifying a track format of the updated track.
 19. Themethod of claim 15, wherein the cache control blocks include trackformat code valid flags indicating whether the track format codes in thecache control blocks are valid or invalid, further comprising: settinginvalid reason bits in a cache control block in response to a writerequest to modify a format of a track.
 20. The method of claim 15,wherein the request for the requested track comprises a first requestand is failed in response to the first request sent on a first channel,further comprising: receiving a second request for the requested trackon a second channel after failing the first request on the firstchannel; staging the requested track into the cache in response to thesecond request and determining that the requested track is not in thecache; and reading metadata for the requested track to determine a trackformat of the requested track staged into the cache to process therequest in response to the request comprising a read request.